An overweight cat in the US has been put on a strict dietary plan which includes three sessions a week on an underwater treadmill.

The six-year-old domestic shorthair named "Buddha" weighed more than 31 pounds (14 kilograms) when he was brought into an animal shelter in Nashville last month.

Volunteer photographer Penny Adams, who was working at the shelter, said she was shocked by the grey-and-white cat’s size and took him to non-profit organisation Cat Shoppe Rescue where he was put on a weight-loss programme.

Buddha is now on a strict diet, and exercises three times a week on an underwater treadmill at the a nearby animal rehabilitation centre.

The fat-fighting feline has dropped two kilograms and can now walk on the treadmill for 12 minutes at a time.

Ms Adams said while the method was unusual, the water held up Buddha’s weight and decreased the pressure on his joints.

"One might think, 'oh cats and water – that’s cruel, how could they do that?' But it really has made a huge difference to his health," she said.

"He’s made incredible progress, he just doesn’t give up. He’s been an inspiration to lots of folks all around the world."